The method is known by which ionic substances are removed from water containing them by the utilization of electrostatic forces using an electric double-layer capacitor.
For example, the specification of U.S. Pat. No. 5,192,432 describes a flow-through capacitor for controlled charge chromatography comprising a spirally wound plurality of adjacent layers including a first electrically conductive backing layer, a first high surface area conductive layer, a first non-conductive porous spacer layer, a second conductive backing layer, a second high surface area conductive layer and a second non-conductive porous spacer layer. It is also shown in the same specification that this capacitor finds application in, for example, the purification of water containing ionic substances, such as sodium chloride.